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I am studying blend modes and I am comfortable with pixels, channels and math equations. I understand that the screen blend mode is calculated as 1 - (1 - c1) * (1 - c2), where c1 and c2 are the colors (or more precisely, the value of each RGB channel).

The question is, why is it called "screen"?

1 Answer 1

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It's called screen because of the analog process it mimics:

From Photoshop Blend Modes Explained :

As an analogy, imagine the selected layer and each of the underlying layers as being 35mm slides, and each slide being placed in a separate projector (one slide for each projector), then all of the projectors are turned on and pointed at the same projector screen…this is the effect of the Screen blend mode.

As the comments note, though, this is a bit too simplistic. The actual screen process effect/equations is more accurately like stacking negatives in an enlarger (or on a flatbed scanner these days).

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  • wouldn't that analog process do additive blending?
    – user253751
    Mar 24 at 10:05
  • @user253751 well yes. Screen is presumably 2 slides on same projector not 2 projectors. Or perhaps their film was logarihmic
    – joojaa
    Mar 24 at 10:30
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    @joojaa Multiple slides in the same projector would be multiplicative blending. Screen looks like film technology with negatives: multiple film negatives in the same photo enlarger.
    – user253751
    Mar 24 at 10:40
  • @user253751 Right screen is multiplicative of inverses so negatives on slide is probably right. So the process is 2 negatives to a film which then is developped for negative and thats the screen. Which is clearly 1-(1-a)(1-b)
    – joojaa
    Mar 24 at 13:34

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